Fibres and their production

ABSTRACT

Continous glass filaments, and fibres obtained by comminuting the filaments and microfibres obtained by flame attenuation of the filaments, are formed of a substantially colourless aluminosilicate glass containing 25 to 52% SiO 2 , 20 to 35% AL 2 O 3  and  0  to  1.5 % FeO and having good biosolubility.

This invention relates to novel fibres and their production wherein thefibres are continuous glass filaments or, in particular, are choppedfibres (made by chopping continuous glass filaments or productscontaining them) or microfibres (namely the fibres obtained by flameattenuation of continuous filaments.

Fibres of these general types (but having different compositions andproperties from those of the invention) are typified by the variousforms of E-glass fibre. These are made as continuous filaments byforming a melt from a homogeneous charge (usually of marbles) in amelter which is heated by gas and/or oil and/or electricity, flowing themelt through a forehearth into a bushing containing a plurality ofextrusion orifices for the melt, and mechanically drawing filamentsdownwardly from the orifices and collecting them as solid endlessfilaments, usually in the form of a bundle.

These filaments, alone or with other filaments, may be used to formfabrics or other sheet materials.

They (or yarns containing them) may be comminuted by any suitablecutting operation so as to provide cut fibres, typically 3 to 25 mmlong, which may be used for, for instance, forming non-woven fabrics ofor containing the chopped fibres, alone or with other fibres.

The initial filaments, or bundles of filaments, may be formed as arather coarse filament or bundle of filament and then subjected to flameattenuation. This process results in remelting the solidified filamentsor bundle by applying a high temperature gas flame, normallysubstantially at right-angles to the filament or bundle, underconditions whereby the primary filament or bundle melts and isattenuated into many fine relatively short fibres. These fibres arecarried by the high velocity gases originating from the flame through aduct and are collected as a web, and optionally sprayed with binder.Flame attenuation can produce fibres which are referred to asmicrofibres (or ultra fine fibres). These flame-attenuated fibres areusually finer and shorter than the cut fibres made by cut filaments andthey have a wider spread of fibre diameters and lengths.

Continuous filaments are non-respirable and therefore may not provide ahealth concern while they are in the form of continuous filaments.However there is a concern when they break and, especially, continuousfibres that are chopped, crushed or otherwise processed duringmanufacture or use may contain small amounts of respirable fibre-likefragments of the same composition. Similarly, microfibres may berespirable or may include respirable fragments. Products containing anyof these fibres (for instance as reinforcement) may be abraded duringuse, or may be cut when being prepared for use, to cause the escape ofglass dust.

E-glass fibres are durable, and respirable E-glass fibres have beenshown to cause advanced fibrosis, lung cancer and mesothelioma in animalstudies. In the evaluation of IARC (International Agency for Research onCancer) from October 2001 it is concluded, that “there is sufficientevidence in experimental animals for the carcinogenicity of specialpurpose glass fibres including E-glass and 475 glass fibres”.

It would therefore clearly be desirable to be able to produce drawnglass filaments (and chopped fibres and microfibres obtained from them)which can be shown to have good biosolubility. It would then be possibleto use such filaments and fibres for uses where a showing ofbiosolubility is necessary or desirable. The filaments and fibres canalso be used as replacements for conventional filaments and fibres(e.g., traditional E-glass) where a showing of biosolubility is notrequired.

Various compositions have been proposed for glass filaments and so itwill be found that there are numerous references in the literature towide ranges of compositions theoretically being converted intocontinuous glass filaments. The technical reality, however, is thatcompositions which are actually going to be converted into filaments ona commercial scale by a convenient apparatus have very narrowly definedproperties, including especially purity and colour, and so in practicefilaments are actually made only from a small number of classes ofcompositions.

For a detailed discussion of compositions suitable for manufacturingcontinuous glass filaments, including chopped fibres and microfibresobtained from them, and of processes and apparatus for making thefilaments, reference should be made to “The Manufacturing Technology ofContinuous Glass Fibres”, Third Edition, by Loewenstein, publishedElsevier 1993, especially pages 26 to 131 (referred to below as“Loewenstein”).

Loewenstein shows in table 4.2 typical compositions of the glasses ofgreatest commercial interest, these compositions being, expressed as %by weight of oxides, E glass C glass A glass S glass R glass E glass Cglass A glass S glass R glass SiO₂ 55.2 65 71.8 65.0 60 Al₂O₃ 14.8 4 1.025.0 25 B₂O₃ 7.3 5 — — — TiO₂ 0 — — — — MgO 3.3 3 3.8 10.0 6 CaO 18.7 148.8 — 9 Na₂O + K₂O 0.5 8.5 13.6 — — Fe₂O₃ 0.3 0.3 0.5 trace — F₂ 0.3 — —— —

Of these, E glass is the glass which is predominantly used for glassfilaments, and cut fibres and microfibres obtained from them.

Loewenstein also mentions others glasses, including a dielectric glasscontaining 45 to 65% SiO₂, 9 to 20% Al₂O₃, 13 to 30% B₂O₃ and 4 to 10%CaO+MgO+ZnO (table 4.3).

The efficiency with which the melt can be formed, and maintained in themolten state, in the furnace is greatly reduced if the melt is notsubstantially colourless. This is because increasing the colour of themelt greatly reduces the transmission of heat energy through the meltwith the result that heating of the melt is much less uniform and sooperation of the process is much more difficult unless the furnace isdesigned specifically, and in a less efficient manner, to allow for theinferior heating of the melt. For instance a process specificallyintended to operate with a coloured melt is described in U.S. Pat. No.6,125,660.

Accordingly, although it is theoretically possible to form a colouredmelt and then to form continuous glass filaments from it by extrusionand mechanical drawing from the orifices of a bushing leading from theforehearth of a furnace, performance of the process is much moreefficient if the melt is substantially colourless. As a result theproduction of continuous filaments (and chopped fibres and microfibresderived from them) of coloured glasses containing these higher amountsof iron is probably, at most, a few hundred tons per annum compared tothe hundreds of thousands of tons per annum worldwide for continuousfibres of substantially colourless glasses such as those listed above inLoewenstein.

Glasses and other vitreous melts containing iron oxide can, however,easily be formed using other melting apparatus, such as a cupolafurnace. The melt cannot be fiberised by extrusion and drawing but itcan be fiberised into wool by centrifugal fiberisation techniques. Onesuch technique involves the spinning cup. Another involves cascadespinners, in which the melt is poured on to the outer surface of one ormore substantially cylindrical rotors which spin about a substantiallyhorizontal axis, whereby fibres are thrown off the surfaces andcollected as wool.

These centrifugal fiberisation techniques are used for products whichare generally known as stone, rock or slag wool, but can also be usedfor glass wool. The melt for this technique is usually relatively crudeand dark and can even contain a few minor undissolved particles or othernon-melt components. These are acceptable in wool made by centrifugalfiberisation because the worst that these can do to the fiberisingprocess is to increase the amount of shot or waste material which ismade on the centrifugal fiberiser. Similarly, iron is acceptable inmelts which may be regarded as being glass melts but which are to becentrifugally fiberised.

The inclusion of iron oxide in the melt (thereby causing the melt to bedark) modifies the melt properties, (which are then suitable forcentrifugal fiberisation), allows cheaper raw materials to be used andimproves the resistance of the fibres to high temperatures. Typicallythe fibres contain 2 to 10%, often around 4 to 10% iron (measured asFeO).

There have been many proposals to improve the biosolubility of theseiron-containing stone, rock or slag fibres which are made by centrifugalfiberisation. Some of the proposals concentrated on solubility of thesevery fine rock, stone or slag fibres at around pH 7.5 (for instanceWO87/05007, WO89/12032, EP-A-459,897, WO92/09536, WO93/22251 andWO94/14717). Others concentrated on solubility at around pH 4.5 (forinstance WO96/14274, WO97/30002, WO97/31870 and WO99/56526). An earlydiscussion of solubilities at both around pH 4.5 and around 7.5 was byChristensen et al in Environmental. Health Perspectives Volume 102,Supplement 5, October 1994 pages 93 to 96. There have been numerousother publications on biosolubility of rock, stone or slag wool but itis believed they do not add significantly to the generality of what isestablished by those listed above.

However the manufacturing constraints, including the requirement thatthe melt should be colourless and should have a temperature-viscosityprofile suitable for extrusion and mechanical drawing are such that noneof these melts can be used to provide continuous glass filaments (andchopped fibres and microfibres) in an economical manner for those useswhere it is required that they should be shown to have goodbiosolubility.

Where attempts have been made to provide improved biosolubility in glassfibres, these attempts have usually involved reducing the amount ofalumina generally to very low values, and optionally adding phosphorousand/or increasing the amount of alkali, for instance as described inEP-A-412,878. Biosoluble glass fibres can therefore be made, but it isdifficult to form drawn continuous filaments and chopped fibres andmicrofibres in an economic manner from such melts.

It would therefore be desirable to be able to provide colourless, drawn,continuous glass filaments (and chopped fibres and microfibres obtainedfrom them) which can be shown to have satisfactory biosolubility andwhich can be made from a substantially colourless melt by convenientextrusion and drawing processes and apparatus. The process and apparatuswould preferably be as close as possible to the conventional E-glassprocesses and apparatus, and with, for instance, only small changes inthe alloys used for defining the extrusion orifices, if necessary).

In the invention we provide fibres of substantially colourlessaluminosilicate glass containing, by weight oxides, SiO₂ 25-52% Al₂O₃20-35% SiO₂ + Al₂O₃ 60-80% FeO  0-1.5% CaO  5-30% MgO  0-20% Na₂O + K₂O 0-15% B₂O₃  0-10% TiO₂  0-5%

In one preferred embodiment, B₂O₃ is present in an amount of 0.5 or1-10%, often 2-10% and preferably 5-10% and most preferably 7-10%. Inthis embodiment, the amount of Na₂O+K₂O is usually below 5% andpreferably below 2% and most preferably zero or below 0.5%.

In another preferred embodiment the amount of B₂O₃ is below 2%, andusually zero or below 0.5% or 1%, and the amount of alkali is above 2%,often 3 to 12% and most preferably 5 to 10%.

The glass is preferably a peralkaline aluminosilicate glass. By this wemean that the mole percentage MgO+CaO+FeO+Na₂O+K₂O is greater than orequal to the mole percentage of Al₂O₃.

Throughout this specification, all amounts are expressed as percentagesby weight calculated on the weight of oxides in the glass (which isidentical with the melt). Iron is expressed as FeO even though some orall of it may be present in the glass as trivalent iron. All percentagesexpressed as a whole number should be interpreted as meaning the exactwhole number, so that 50% means 50.0%.

The elements quantified and listed above preferably provide at least.90% and usually at least 95% and preferably at least 98% (by weight ofthe oxides) of the glass, and often they provide 100% of the glass.There can be trace amounts of other elements and there can be deliberateadditions of other elements (up to 100%), provided this does notdeleteriously influence the properties of the glass. Such other elementswhich may be included are, for instance, BaO, ZrO₂, Li₂O, F₂, ZnO, andP₂O₅. Usually the maximum amount (as oxide) of any element other thanthose quantified above is below 2% and usually not more than 1%, byweight oxides. The optional ingredients generally do not include Y₂O₃,La₂O₃ or CeO₂.

Although the amount TiO₂ may be zero or low (for instance below 3%) itis often desirable to include one, two or three (or more) oxidesselected from TiO₂, ZrO₂, BaO, ZnO and Li₂O generally in a total amountof 2-10%, each generally being in an amount of 0.1 to 5%, often 1 to3%., in order to adjust melt properties, especially the liquidustemperature. The addition of BaO, for instance, in an amount of at 0.5to 5%, (and optionally with TiO₂ and/or ZrO₂) can be particularlyuseful. This applies both with fibres containing 2-10% B₂O₃ and with thelow or zero B₂O₃ fibres described above. These additions improve themechanical properties of the fibres and influence the liquidustemperature and viscosity profile.

In all the fibres of the invention, the amount of FeO is usually below,or not more than, 1.0% and preferably not more than 0.5%. Often it isnot more than 0.3%. It may be zero.

The amount of SiO₂ is usually not more than 0.50% and often not morethan 48%. It is usually at least 35 or 40%, and often is at least 43% or45%.

The amount of SiO₂+Al₂O₃ is usually not more than 78% and preferably notmore than 75%. Often it is at last 60% and is preferably at least 63% or65%.

The amount of CaO is usually at least 10%. Often it is not more than22%, frequently not more than 20%.

The amount of MgO is usually at least 2%. Often it is not more than 12%and preferably not more than 10%. Often it is not more than 8% andprefearbly it is not more than 6%.

The amount of CaO+MgO is often at least 15% but below 25%. The amount ofCaO, by weight, is usually at least twice the amount of MgO.

The amount of Na₂O+K₂O is often at least 2%, and often at least 3.5% andusually at 5%, but preferably not more than 10%. However, as explainedabove, the amount of alkali is often at or near zero when the fibrescontain at least 2% B₂O₃.

The amount of TiO₂ is usually not more than 3% and often not more than1%, and often it is below 0.5%, typically zero.

Depending upon the predominant criteria (for instance optimummanufacturing conditions or intended biosolubility or other propertiesof the final products) the fibres of the invention tend to fall intofive classes.

One class in the B₂O₃-containing fibres which contain little or noalkali as discussed above (referred to below as class A fibres).

A second class is the alkali-containing fibres which contain little orno B₂O₃, as discussed above. (referred to below as class B fibres).

A third class of fibres are referred to as class C fibres and containSiO₂ 43-52% Al₂O₃ 25-35% SiO₂ + Al₂O₃ 70-80% FeO  0-1.5% CaO  5-30% MgO 0-20% B₂O₃  0-10% Na₂O + K₂O  0-15% TiO₂  0-5%

Within these class C fibres, iron, calcium, magnesium, alkali andtitania (and boron, if present) are preferably all as discussed above,and these elements preferably provide at least 95%, and often 98 or100%, of the glass.

The amount of SiO₂ is preferably not more than 50% and most preferablynot more than 48%. Usually it is at least 44% or 45% and preferably atleast 46%. The amount of Al₂O₃ is generally at least 26.5% or 27%.Instead of or in addition to selecting SiO₂ and/or Al₂O₃ within thesepreferred ranges, preferably the amount of SiO₂+Al₂O₃ in these class Cfibres is at least 72 or 73% and often below 78% or 75%.

A fourth class of fibres, which may be boron-free or boron-containing,are referred to as class D fibres and contain SiO₂ 35-45% Al₂O₃ 20-30%SiO₂ + Al₂O₃ 60-75% FeO  0-1.5% CaO  5-30% MgO  0-20% B₂O₃  0-10% Na₂O +K₂O  0-15% TiO₂  0-5%

In these class D fibres the amount of SiO₂ is often at least 38% andgenerally at least 40%. The amount of SiO₂ is often not more than 44%,preferably not more than 42%. The amount of Al₂O₃ is generally at least22% and preferably at least 23%. The amount of SiO₂+Al₂O₃ is generallyat least 65% and preferably at least 67 or 68% but often not more thanabout 72%. The quantified elements (including boron if present)generally provide at least 95%, and often 98-100% of the glass, asdiscussed above.

A fifth class of fibres within the invention are is boron-free orboron-containing fibres and are referred to as class E fibres andcontain SiO₂ 30-40% Al₂O₃ 25-35% SiO₂ + Al₂O₃ 60-75% FeO  0-1.5% CaO 5-30% MgO  0-20% B₂O₃  0-10% Na₂O + K₂O  0-15% TiO₂  0-5%

Each of classes C, D and E can be sub-divided into preferred fibreswhich contain B₂O₃ but little or no alkali, and preferred fibres whichcontain alkali but little or no B₂O₃, as discussed above.

The inclusion of BaO and/or TiO₂ and/or ZrO₂ can be advantageous foreach class, as discussed above.

The class C fibres are particularly valuable because of thebiosolubility and their mechanical properties and theirviscosity-temperature profile. They can generally be produced easily byextrusion at a relatively high temperature and high viscosity.

The class D fibres have particularly good biosolubility and mechanicalproperties and are best manufactured at lower process temperatures andlower viscosities.

The class E fibres are of particular value for specialised applications.Again they have good biosolubility.

Substantially all fibres within each of these classes have goodbiosolubility and this can be confirmed by subjecting the fibres to abiosolubility test (as discussed below).

The various fibres defined above are preferably made by extrusion andmechanical drawing (in contrast to centrifugal extrusion) in a mannersimilar to conventional E glass manufacture. Preferred fibres aremicrofibres as discussed above, cut fibres made by cutting continuousfilaments into staple fibres, and the continuous filaments. Theinvention also includes products which consist of or are reinforced byfilaments or cut fibres or microfibres made from such filaments andwhich are liable to be cut or abraded during installation, manufactureor use, with possible release of glass dust.

In this specification, references to biosolubiilty are particularlyrelated to in-vivo biopersistence as measured according to theEU-guidelines (European Commission. (1997).a) Biopersistence of fibres.Intratracheal Instillation. ECB/TM/17[rev.7], Directorate General, JointResearch Centre. B). Biopersistence of fibres. Short-term exposure byinhalation. ECB/TM/26[rev.7], Directorate General, Joint ResearchCentre). In these tests rats are exposed to fibres, size-selected to berat-respirable and the elimination of fibres from the rat lungs isfollowed with time. As a result the biosolubiilty or the biopersistenceis described by the half-time, T₅₀. The fibres in this invention willtypically have a half-time for elimination of long fibres (>20 μm) afterinhalation of less than 20 days, preferably less than 15 days and mostpreferable less than 10 days. The fibres in this invention willtypically have a half-time for elimination of long fibres (>20 μm)and/or of WHO fibres (defined as fibres having a diameter <=3 μm, alength >5 μm and a length to width ration of >=3:1) after intratrachealinstillation of less than 80 days, preferably less than 60 days and mostpreferably less than 40 days. IARC (October 2001) concluded that “anumber of studies in rates have suggested a correlation between thebiopersistence of long fibres (>20 μm) and their pathogenicity withrespect to lung fibrosis and thoracic tumours”.

Biosolubility may also be assessed measuring the in-vitro dissolutionrate, e.g., such as described in [European Insulation Manufacturers'Association (EURIMA). (1998). Test guideline for “In-vitro acellulardissolution of man-made vitreous silicate fibers (pH 7.4 and pH 4.5)”,Draft 11]¹. IARC (October 2001) conclude that “the most informativestudies employ flow-through systems using balanced salt solutions atphysiological pHs likely to be encountered in the intrapulmonaryenvironment. The results from such studies have shown correlations withrates of removal of long fibres from the lung in short-termbiopersistence assays”.

The fibres in the present invention preferably have in-vitro dissolutionrates at pH 4.5 measured in a flow-through set up as described in[European Insulation Manufacturers' Association (EURIMA). (1998). Testguideline for “In-vitro acellular dissolution of man-made vitreoussilicate fibers (pH 7.4 and pH 4.5)”, Draft 11] of at least 200 ng/cm²h,preferably at least 300 ng/cm²h, and most preferably at least 400ng/cm²h.

The glasses have a tetrahedral structure formed predominantly by siliconand aluminium with atoms bridged by oxygen atoms. A preferred class offibres according to the invention are free of boron or contain less than2% B₂O₃ and the amount of SiOSi bridges in the glass is not more than18% and preferably not more than 17%, and generally not more than 15%(but usually above 10 or 12%), when calculated by the protocol definedbelow. Fibres having this number of SiOSi bridges (or less) haveparticularly good biosolubility.

Varying the proportions of the elements will influence the calculatedSiOSi value and the T_(liq) and the temperature-viscosity curve. Thecommon general knowledge of the effect of compositional changes onT_(liq) and the temperature viscosity curve, and the teachings belowabout the calculation of SiOSi linkages, will allow appropriateselection of the content of the materials.

SiO₂ must be at least 25% and is often above 30% and usually above 35 or40%. It must not be above about 50% and often it is below 48%. Reducingthe amount of SiO₂ tends to decrease the calculated SiOSi value anddecrease the viscosity at any specific temperature whilst increasingSiO₂ has the opposite effect.

The amount of Al₂O₃ must be at least 20% and is often at least 23% andusually at least 25%. It must be not more than 35% and is often below32% and usually below 30%. Reducing the amount of Al₂O₃ tends toincrease the calculated SiOSi value and decrease the viscosity at anyspecific temperature whilst increasing Al₂O₃ has the opposite effect.

The amount of CaO must be at least 5% and is often at least 10%. It mustbe below 30% and is often below 25% and usually below 20%. MgO isoptional but is often present in an amount of at least 2% usually atleast 5%. It must be below 20% and is often below 10%. To some extentCaO and. MgO can be considered together and are generally present in anamount of 10 to 40%, often 10 to 25%. In general, reducing themindividually or together tends to increase the calculated SiOSi valueand increase the viscosity at any specific temperature whilst increasingthem has the opposite effect.

Na₂O+K₂O can be considered together and the combined amount is usuallyat least 0.5%, or 2% and is often at least 3%. It must not be above 15%and is often below 12% and usually below 10%. Usually the amount of Na₂Ois 5 to 10%. Reducing Na₂O+K₂O tends to increase the calculated SiOSivalue whilst increasing them has the opposite effect. When B₂O₃ ispresent, the amount of alkali may be low or zero.

The amount of FeO is critical and must be below 1.5% and is usuallybelow 1.0%. Preferably it is below 0.7%.

A very small amount of iron is often convenient (because it allows theuse of raw materials which have trace iron content) and may improveperformance due to the effect it has on radiation properties duringmelting. Accordingly, although the amount of iron can be zero or trace,usually it is at least 0.1% and is typically in the range 0.2 to 0.5%.

Since it is desirable that the fibres can be made using furnaces andextrusion techniques substantially the same as those which areconventional for E-glass manufacture, the melt preferably has anappropriate viscosity-temperature relationship and this is convenientlydiscussed by reference to the liquidus temperature, T_(liq).

Protocols for determining T_(liq), viscosity and other temperatures aregiven below.

The viscosity at T_(liq) is preferably at least 300 poise and preferablyat least 500 poise and most preferably at least 900 or 1000 poise.Preferably viscosity at T_(liq) is at least 1020 poise, often at least1050 poise and preferably at least 1100 poise. It is not necessary forit to be very much higher than this and so it is usually below 10000poise, preferably below 5000 poise and values below 2000 poise, andoften below 1500 poise, are often preferred.

An alternative way of indicating that the viscosity at T_(liq) is at thechosen viscosity (e.g., 900 poise) is to indicate that the temperatureat which the viscosity is 900 poise is at least T_(liq), and preferablyis above T_(liq) by at least 5° C. and usually at least 10 or 20° C. upto 50° C. or more. It is usually unnecessary for it to be more than 100°C. or 150° C. above T_(liq).

When the fibres are to be continuous filaments, it is preferred that theviscosity at T_(liq) should be at least 900 poise, but lower viscositiesare suitable for the manufacture of microfibres.

The temperature of the melt for extrusion is preferably above T_(liq) inorder to minimise or avoid incipient crystallisation in the melt orfilaments before or during extrusion. Accordingly the melt beingextruded normally has a temperature at least 30° C. above T_(liq) andoften at least 50° C. above T_(liq). Thus the melt temperature isusually at least T_(liq)+50 during extrusion.

A preferred additional feature, which is a particular benefit of theclass A fibres, is that the melt is what is frequently referred to as a“strong” melt and therefore crystallises very slowly and so will staymolten during extrusion even after the temperature of the extruded melthas dropped below T_(liq), the liquidus temperature.

The difference in heat capacity between the glass and the melt at Tg istherefore preferably low. It is therefore preferred that the differencein heat capacity in Jg⁻¹K⁻¹ at Tg is less than 0.40 and is preferablyless than 0.38. The difference is preferably not more than 0.35 and mostpreferably not more than 0.33. In practice it normally is above 0.2 or0.25. Tg is preferably quite low, e.g., below 800°, often below 750° C.,and preferably in the range 500-700° C., often 550-650° C.

The difference in heat capacity can be determined, and Tg can bedetermined (for instance at a cooling rate of 10K/min), in accordancewith Reviews in Minerology, Volume 32, Structure Dynamics and Propertiesof Silicate Melts by J. F. Stebbins et al, Chapter 1 pages 1-9 byMoynihan and Chapter 3 pages 72-75 by Richet et al. Examples of typicalplots are in Thermochimica Acta, 280/281, (1996) 153-162 by Moynihan etal. Temperatures are measured by Differential Scanning Calorimetry.

Since the extrusion temperature may be above T_(liq), and sinceincreasing the spinning temperature significantly above typical E-glassvalues (up to around 1400° C.) can cause accelerated wear of thebushings, it is preferred that T_(liq) is below not more than 1380° C.,preferably below 1350 or 1320° C., and generally below 1300° C. Valuesof below 1275° C. or, especially, 1250° C. are particularly preferred.Generally therefore T_(liq) is at least 1100° C. and usually above 1130°C. Often it is above 1170° C.

The extrusion temperature (i.e., the temperature of the melt as it isextruded through the extrusion orifices should not be too high or elseit creates particular demands on the materials of which the orifices areformed. Usually the temperature is below 1500° C., preferably below1450° C.

The viscosity of the melt preferably is not too high during extrusion asotherwise it may be difficult to achieve satisfactory extrusion anddrawing. Accordingly the viscosity at T_(liq+50) and preferably at thetemperature of extrusion should normally not be more than 10000 poise,preferably not more than 5000 poise and usually not more than 3000poise. Often it is not more than 2000 poise.

In practice melt temperature may vary a little during the process. Asexplained, it should normally always be at least T_(liq+50) in orderthat there is no crystallisation and the viscosity is always below 10000poise and preferably below 3000 poise.

The viscosity should never fall below 200 poise and is preferably in therange 300 to 1000, most preferably 400 to 800 (typically around 500poise) at the highest temperature which is probable for the melt beingextruded. This maximum temperature is usually at least 100° C. aboveT_(liq), often in the range 120 to 200° C. above T_(liq), typicallyaround 150° C. above Tliq. Accordingly the lowest viscosity at thetemperature of extrusion is usually above 200 poise and often above 500poise. In practice therefore extrusion is generally conducted at atemperature whereby the viscosity is in the range, typically, 200 to10000 poise, often 500 to 5000 poise.

In order to facilitate convenient operation of the furnace and to givesome flexibility in the temperature control while still having asuitable viscosity during extrusion it is desirable that the temperaturerange between the highest and lowest convenient spinning viscosities isat least 50° C. and it can even be up to 100° C. It can be higher suchas 120 or 150° C., or even 200° C. but this is generally unnecessarysince control within, for instance, a range of around 70 or 80° C. isusually adequate. Thus, if the extremities of working viscosities are5000 to 200 poise then the difference in temperatures for these valuesshould be in the quoted range of 50 to 100° C. but if, as is more usual,the viscosity range is 2000 to 500 poise or even less, for instance 1500to 600 poise, then the difference of from 50 to 100° C. should apply tothis range of viscosities.

A typical combination of preferred values is

-   -   T_(liq) is 1200 to 1250° C.,    -   viscosity at T_(liq) is 900 (preferably above 1000 and often        above 1100) up to 1500 or 2000 poise,    -   temperature for a viscosity of 900 poise or preferably 1000        poise, or more, is 0 to 70° C. preferably 5 to 50° C. above        T_(liq),    -   T_(liq+50) and/or temperature for viscosity of 2000 poise is        1250 to 1300° C.,    -   and temperature for a viscosity of 200 poise (or preferably 500        poise) is 1340 to 1450° C., and the temperature difference        between 5000 poise and 500 poise (or preferably between 2000        poise and 500 poise) is from 50 to 150° C.

When a curve is plotted of viscosity against temperature for therelevant materials, it is immediately apparent that a small increase intemperature gives a much larger reduction in viscosity at lowertemperatures than at higher temperatures. The quoted limits take accountof this and ensure that the working range of viscosities (generally 5000to 500 poise) is spread over a usefully wide temperature range(typically 50 to 150° C.) and that the liquidus temperature is at anappropriate value such that the viscosity is appropriate for spinning ata temperature only 30 to 50° C. above T_(liq).

The invention includes fibres which are continuous filaments formed ofthe various generic definitions of fibres, including each of class A, B,C, D and E fibres, and preferred glasses described above. The inventionincludes methods of making these continuous filaments by providing ahomogeneous charge in a melter, melting this, flowing the melt through aforehearth into a bushing containing a plurality of extrusion orificesfor the melt, and drawing filaments downwardly from the orifices andsolidifying the filaments by cooling. The drawn filaments typically havea median diameter of above 5 μm and usually above 7 μm and usuallyaround 9 μm, although it can be up to 25 μm or 50 μm or more.

The invention includes yarn formed from a bundle of these filamentsalone, or with other filaments. The invention includes fabrics formedfrom such yarn or other filaments. The invention also includes themethod of forming the fabrics.

The fibres of the invention can have mechanical properties similar to Eglass fibres but with increased biosolubility, especially whendetermined in vitro at pH 4-5 or in vivo in the lung. They can havesimilar dielectric properties to E glass, especially when the fibrescontain 2-10% B₂O₃.

The invention also includes cut fibres formed from such filaments (orfrom yarn containing such filaments), wherein the filaments are formedof the various generic and preferred compositions described above. Thesecut fibres have diameters as indicated above for filaments and they havelengths that are usually above 3 mm and preferably above 5 mm, forinstance at least 10 mm typically up to 25 or 50 mm.

The invention also includes microfibres formed from the various generic(including classes A, B, C, D and E) and preferred compositionsdescribed above, and in particular formed by flame attenuation ofcontinuous filaments formed from such compositions, by the generalmethod described above. The microfibres generally have a length basedmedian diameter of below 2.5 μm and usually below 2 μm. It should benoted that the diameter of microfibres is less than the diameter ofconventional mineral wool, that is to say the wool formed from staplefibres formed by processes such as the spinning cup process or theDusenblasten process. The staple fibres of glass wool normally have alength based median diameter of ≧3 μm, typically 3-3, 5 μm.

The processes for extruding the filaments to make the cut fibres and themicrofibres are less sensitive to deviations from optimum meltproperties, because it is not necessary to extrude and draw thefilaments with the precision needed for optimum continuous filamentmanufacture. This is advantageous in the invention since the need forbiosolubility in glass fibres made by extrusion and mechanical drawingis greatest when the drawn fibres are to be converted to cut fibres ormirofibres. Accordingly the necessary solubility can be achieved in suchproducts from a melt having properties adequate for production of thesefibres, without the need to optimise the melt properties to thestandards required for normal E glass continuous filament production.

The invention also includes non-woven fabrics and other sheet materials,such as filter cloths, formed from the microfibres or from the cutfibres. The invention also includes fibre reinforced products whereinthe fibre reinforcement is continuous filaments, cut fibres ormicrofibres in a polymeric or other matrix or wherein the fibres arebonded or woven together, and wherein the products are liable to beabraded in use (e.g., as brake linings) or cut in use, with theconsequential risk of escape of glass dust or fibrils.

The invention also includes the use of the continuous filaments or otherfibres as biosoluble fibres, and in particular the use of the fibres forapplications where it is required to show that the fibres havebiosolubility. The invention is of particular value when the fibres aremicrofibres. In particular, the invention includes the use of the fibresfor an application where they are shown to be biosoluble (i.e.,biodegradable in the lung). The invention also includes the use of amelt having the selected analysis and properties to form such fibres.

The invention also includes a package or other product containing thecontinuous filaments or other fibres and which is labelled or associatedwith advertising referring to the biosolubility of the fibres.

The invention also includes a method of making the continuous filamentsor other fibres comprising selecting a composition having the requiredtemperature viscosity relationship and having the required biosolubility(when present as fibres) and forming fibres from the composition. Theselection may be conducted solely by theoretical identification of anappropriate composition based on previous experience or the selectionmay be made on the basis of examining the properties of variouscompositions and fibres made from them and selecting a compositionhaving the required properties for the melt and the fibres.

Determination of Liquidus Temperature

This is determined in accordance with ASTMC-829-821 Method B.

Determination of Viscosity

All viscosities mentioned herein are determined by measurement asdescribed at Table 1, No. 4, of DIN 53019 Part 2.

Determination of Temperature

All temperatures are determined by thermo-couple measured on the melt inthe bushing, which in practice amounts to measuring the temperaturewhile entering the bushing.

Biosolubility

This may be determined either directly on flame attenuated fibres or bycomminuting filaments to a consistent small standard size and thenapplying the methods described above or the protocols described inChristensen, et al. “Effect of chemical composition of man-made vitreousfibres on the rate of dissolution in vitro at different pHs”. Environ.Health Perspect, 1994, 102(5), 83-86, or in Guldberg, et al. “Method fordetermining in vitro dissolution rates of man-made vitreous fibres”,Glastech. Ber. Glass Sci. Technol, 1995, 68, No6, p. 181-187.

Instead of using an in vitro test, in vivo tests known for assessing thebiosolubility of man-made vitreous fibres may be used. Whatever test isused, preferably it determines the solubility at around pH 4.5 and, inparticular, it preferably indicates solubility in the environment ofmacrophages in the lung.

Calculation of Amount of SiOSi Bridges

The chemical analysis of the glass guarantees that the predominantstructure will be a tetrahedral structure formed by silicon andaluminium ions, and the amounts much be such that the calculated amountof SiOSi bridges is not more than 18% of the total oxygen bridges.

The chemical composition is known and is such as to guarantee that meltis what is often referred to as a peralkaline aluminosilicate glasswherein all the alumina ions are charge balanced by alkali metal oralkaline earth metal ions.

The calculation for fibres which are free of boron or contain less than2% boron is based on the following assumptions:

Alumina is tetrahedrally coordinated and charge balanced.

The charge balancing of aluminium is made in accordance with Bottingaand Weill “The viscosity of Magmatic Silicate Liquids: A model forcalculation” AM J Science, 272 (May 1972) pp 438-4.75, Hess “The role ofhigh field strength cations in silicate melts” Advances in Physical.Geochemistry—Physical Chemistry of Magmas 9 (1991) Chapter 3, pp152-185, or Mysen, “Structure and properties of silicate melts”,Elsevier Science Publishers (1988) Chapter 3, pp. 79-146 and chapter 8,p 266.

Alumina is placed in fully polymerised sites; all non-bridging oxygensare placed around silica and titanium ions.

The remaining network can be treated as tecto-aluminosilicate.

The calculation sequence is:

-   1. Calculation of distribution of charge balancing cations-   2. Calculation of Q (degree of aluminium avoidance) based on charge    balancing of aluminium-   3. Allocation of non-bridging oxygens to silica and titanium-   4. After allotting the non-bridging oxygens to silica, the remaining    glass is treated as a tecto-aluminosilicate glass.

The chemical composition (mol %) is assumed known. Calculation oftetrahedral alumina-units is done according to the procedure describedby Bottinga and Weill (X_(bw)).

Lee and Stebbins introduce the variable Q, which describes the degree ofaluminium avoidance (avoidance of Al-Q-Al linkages). Q=0 for noavoidance and Q=1 for total avoidance. It is found that the Q valuevaries from approx. 0.85 when. ½Ca²⁺ is charge-balancing aluminium toapprox. 0.99 when Na⁺ is the charge-balancing ion. The fraction ofalkali and earth alkali balanced aluminium (R_Al) is calculated:${R\_ Al} = \frac{{NaAlO}_{2{({bw})}} + {KAlO}_{2{({bw})}}}{\begin{matrix}{{NaAlO}_{2{({bw})}} + {KAlO}_{2{({bw})}} +} \\{2 \cdot \left( {{{CaAl}_{2}O_{4{({bw})}}} + {{MgAl}_{2}O_{4{({bw})}}}} \right)}\end{matrix}}$Q=R_Al.0.99+(1−R_Al).0.85The NBO/T ratio (non-bridging oxygens (NBO) per tetrahedral coordinatedcations (T)) is calculated from the molar composition (X_(mol)):NBO=2·(FeO_(mol)+CaO_(mol)+MgO_(mol)+Na₂O_(mol)+K₂O_(mol)—Al₂O_(3(mol)))T=SiO_(2(mol))+TiO_(2(mol))+2.Al₂O_(3(mol))As each tetrahedrally coordinated cation has four oxygen linkages, thefraction of non-bridging oxygen of the total number of oxygen linkagesis: $N_{{Si}\text{-}O\text{-}R} = \frac{NBO}{4 \cdot T}$This calculated fraction of oxygen bonds is allotted to silica andtitanium as non-bridging. Those bonds are substracted the silica networkand the remaining fully polymerised network is found asX_(si)=[(SiO_(2(bw))+TiO_(2(bw))−0.5(FeO_((bw))+CaO_((bw))+MeO_((bw))+Na₂O_((bw))+K₂O_((bw)))]X_(Al)=(KAlO_(2(bw))+NaAlO_(2(bw))+2(CaAl₂O_(4(bw))+MgAl₂O_(4(bw)))]The fraction of aluminium and silica (+titanium) in the network is then:$\begin{matrix}{{Si}_{network} = \frac{X_{Si}}{X_{Si} + X_{Al}}} & {{Al}_{network} = \frac{X_{Al}}{X_{Si} + X_{Al}}}\end{matrix}$Based on NMR-measurements Lee and Stebbins, the degree of aluminiumavoidance in aluminosilicated glasses. “Am Mineral” 84 (1999), pp937-945, introduce the variables η, and β for the calculation of thedistribution of linkages:η{square root}{square root over (1−Q)}β={square root}{square root over (1+4.Si_(network).Al_(network).(η²−1))}By use of β, three types of oxygen linkages in fully polymerised meltsare calculated as: $\begin{matrix}{X_{{Si}\text{-}O\text{-}{Al}} = {4 \cdot {Si}_{network} \cdot {Al}_{network} \cdot \frac{1}{\beta + 1}}} \\{X_{{Si}\text{-}O\text{-}{Si}} = {{Si}_{network}\left( {1 - {2\frac{{Al}_{network}}{\beta + 1}}} \right)}} \\{X_{{Al}\text{-}O\text{-}{Al}} = {{Al}_{network}\left( {1 - {2\frac{{Si}_{network}}{\beta + 1}}} \right)}}\end{matrix}$The total oxygen linkages distribution is found by normalising thenetwork linkages by(1-N_(Si—O—R))N_(Si—O—Al)═X_(Si—O—Al).(1-N_(Si—O—R))N_(Si—O—Si)═X_(Si—O—Si).(1-N_(Si—O—R))N_(Al—O—Al)═X_(Al—O—Al).(1-N_(Si—O—R))N_(Si—O—R)═N_(Si—O—R)

The value is considered to be accurate to ±0.005 and so 0.17% (i.e.,17%) is indicated by a calculated value of above 0.165 to below 0.175.

After applying this calculation, the calculated value for SiOSi(N_(Si—O—Si)) should be 0.18 or less, namely 18% or less of the oxygenbridges are SiOSi bridges. Often the amount is below 17% and preferablybelow 15 or even 14%. Normally it is above 10% and often above 12%.

To make the fibres, a homogeneous charge is usually used to form themelt in the melter and this may be a charge of homogeneous marbles orother pellets previously formed in a prior melting operation and/or maybe a blend of finely ground particulate materials which are melted inconventional manner with appropriate agitation, such as bubbling, toensure a homogeneous melt. Typically the melter can be substantially thesame as is conventional in the production of E-glass and as described byLoewenstein (but with modification of the bushings around the spinningorifices, if necessary, to provide adequate temperature and corrosionresistance). The melter will be designed according to whether it ismelting raw materials or marbles, or a combination thereof. The depth ofthe melt in the melter can be, for instance 20 to 120 cm.

The charge is heated by gas and/or oil and/or electricity (usually gasor oil optionally with some electrical heating as a supplement) and notby solid carbon. The use of solid carbon (as is conventional in theproduction of mineral wool) is inappropriate. In particular, it isdesirable that the conditions are not so reducing that any iron ispresent as metallic iron which destroys the bushing and may interferewith the filament formation. This is in contrast to conventional rock,stone and slag wool production where metallic iron in the melt isunwanted but acceptable.

The melt flows from the main melter through a region conventionallyreferred to as a forehearth into a bushing, all of which can be ofconventional construction as described by Loewenstein. Likewise, theextrusion orifices and the drawing technique and the processes to whichthe filaments are subjected during drawing may be conventional, asdescribed by Loewenstein. Naturally it is necessary to select theappropriate orifice sizes and the precise drawing, cooling and sizing orother conditions so as to obtain filaments having the desired diameterand physical properties such as tensile strength, elastic modulus andelongation at break.

The filaments are, as usual, extruded as a bundle of a large number offilaments, usually at least 50 and often more than 200 up to forinstance 4000. Usually the filaments are twisted or bundled intomultifilament yarn although they may be maintained as monofilaments, inconventional manner.

The filaments (as monofilaments or yarn) may, e.g., be used for purposesfor which E-glass filaments are used at present. Examples include mostcommon textiles, mufflers, exhaust systems.

They (as monofilments or yarn) may be cut or otherwise comminuted andused for any of the purposes for which cut E-glass filaments and yarnare used at present. Examples include composite materials.

Alternatively, the filaments may be extruded in a coarser form and thebundle, after solidification, may be subjected to flame attenuation soas to form microfibres which are collected on a collector as a web, forinstance for use as filters.

Two examples of suitable compositions for use in the invention to makecontinuous filaments, cut fibres or microfibres are Composition 1 2 SiO₂(wt %) 46.4 43.0 Al₂O₃ 27.5 25.7 TiO₂ 0.0 0.0 FeO 0.0 0.0 CaO 14.7 18.8MgO 2.8 5.0 Na₂O 7.6 6.3 K₂O 0.9 1.2 SiOSi 0.169 0.121

Composition 1 has a particularly low difference in heat capacity at Tgand gives fibres of good biosolubility and allows excellent spinning,but is spun at a relatively high temperature and viscosity. Composition2 has lower viscosity and gives even better biosolubility.

Each of the compositions is formed into a melt, and then into fibres,using a laboratory version of a conventional E glass furnace, extrusionand mechanical drawing apparatus.

Other examples, with Tg, T_(liq), and flow-through dissolution rate v(nm/day at 37° C. in Gambles liquid at pH 4.5, calculated on Si insolution) are 3 Wt % 3 4 5 6 E SiO₂ 46.5 44.6 42.8 41.5 52.2 Al₂O₃ 27.328.4 25.6 26.5 16.4 TiO₂ <0.1 <0.1 <0.1 <0.1 <0.1 FeO <0.1 <0.1 <0.1<0.1 <0.1 CaO 14.9 15.2 18.7 18.9 18.9 MgO 2.8 3.0 5.0 5.1 5.0 Na₂O 7.2<0.1 6.3 <0.1 <0.1 K₂O 0.9 <0.1 1.2 <0.1 <0.1 P₂O₅ <0.1 <0.1 <0.1 <0.1<0.1 B₂O₃ <0.1 8.4 <0.1 7.7 7.4 Tg (° C.) 709 728 696 702 688 T_(liq) (°C.) 1180 1231 1200 1230 1122 V_(period), day 1-4 37.9 17.3 59.3 60.6 0.0V_(start), day 14 45.8 23.1 60.2 67.6 1.1

The Si—O—Si values for compositions 3 and 5 are 0.17 and 0.12respectively. The great improvement in bisolubility of fibres 3 to 6,relative to E glass, is clear.

Comparisons of resistance to strong acid, resistance to strong alkali,tensile strength, dielectric constant and electrical conductance offibres 4 and E showed that fibre 4 is a fibre which is a satisfactoryreplacement for the normal uses of E glass but with the advantage ofbeing biosoluble.

Other suitable fibres, additional to fibres 1 to 6 include amodification of fibre 4 wherein the amount of CaO is reduced to 13% and2.2% BaO is added, and a modification of fibre 5 in which alkali ispartly replaced by up to 2% of one or more of TiO₂, ZrO₂, BaO, ZnO andLi₂O.

1. Fibres of substantially colourless aluminosilicate glass wherein thefibres are selected from continuous filaments, cut fibres andmicrofibres, characterised in that the glass contains, by weight oxides,SiO₂ 25-52% Al₂O₃ 20-35% SiO₂ + Al₂O₃ 60-80% FeO  0-1.5% CaO  5-30% MgO 0-20% Na₂O + K₂O  0-15% TiO₂  0-5% B₂O₃  2-10%


2. Fibres according to claim 1 in which the glass contains, by weightoxides, SiO₂ 43-52% Al₂O₃ 25-35% SiO₂ + Al₂O₃ 70-80% FeO  0-1.5% CaO 5-30% MgO  0-20% Na₂O + K₂O  0-15% TiO₂  0-5% B₂O₃  2-10%


3. Fibres according to claim 1 in which the glass contains, by weightoxides, SiO₂ 35-45% Al₂O₃ 20-30% SiO₂ + Al₂O₃ 60-75% FeO  0-1.5% CaO 5-30% MgO  0-20% Na₂O + K₂O  0-15% TiO₂  0-5% B₂O₃  2-10%


4. Fibres according to claim 1 in which the glass contains, by weightoxides, SiO₂ 30-40% Al₂O₃ 25-35% SiO₂ + Al₂O₃ 60-75% FeO  0-1.5% CaO 5-30% MgO  0-20% Na₂O + K₂O  0-15% TiO₂  0-5% B₂O₃  2-10%


5. Fibres according to claim 1 in which the glass contains, by weightoxides, SiO₂ 40-48% Al₂O₃ 23-30% SiO₂ + Al₂O₃ 65-78% FeO  0-1% CaO10-20% MgO  2-10% Na₂O + K₂O  0-10% TiO₂  0-3% B₂O₃  2-10%


6. Fibres according to claim 1 in which the amount of Na₂O+K₂O is notmore than 2%.
 7. Fibres according to claim 1 in which the glass containsone or more oxides selected from TiO₂, BaO, ZrO₂, ZnO and LiO₂ in atotal amount of 2 to 10%.
 8. Fibres according to claim 1 in which theviscosity at T_(liq) is at least 900 poise.
 9. Fibres according to claim1 in which the viscosity at T_(liq)+50 is not more than 10000 poise. 10.Fibres according to claim 1 in which the temperature for a viscosity of500 poise is not more than 1450° C. and is more than 50° C. above thetemperature for 5000 poise.
 11. Fibres according to claim 1 in whichT_(liq) is below 1320° C.
 12. Fibres according to claim 1 in which thedifference in heat capacity between the glass and the melt from whichthe glass is formed is not more than 0.35 Jg⁻¹K⁻¹.
 13. Fibres accordingto claim 1 in the form of continuous filaments.
 14. Fibres according toclaim 1 in the form of chopped fibres obtained by chopping continuousfilaments.
 15. Fibres according to claim 1 in the form of microfibresobtained by flame attenuation of continuous filaments.
 16. Fibresaccording to claim 1 in which the glass is a peralkaline glass.
 17. Amethod of forming fibres according to claim 1 comprising forming a meltof the composition from a homogeneous charge in a melter heated by a gasor oil or electricity or combination thereof, flowing the melt through aforehearth into a bushing containing a plurality of extrusion orificesfor the melt and drawing filaments downwardly from the orifices andcollecting the filaments, and optionally converting the filaments intocut fibres or microfibres. 18-19. (canceled)
 20. A package containingfibres according claim 1, and a label or other information referring tothe biosolubility of the fibres. 21-34. (canceled)